Depth- and size-dependent rhythms of animal emergence in an estuary

• Published in: The Journal of the Acoustical Society of America 2006-11, Vol.120 (5_Supplement), p.3059-3059
• Main Authors: Sato, Mei, Jumars, Peter A.
• Format: Article
• Language: English
• Subjects: Brackish; Gadus morhua; Neomysis americana
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4787308

Among migrating crustaceans, some species inhabiting shallow waters stay very close to the bottom or burrow into the sediments during the day and come up to the surface at night. This behavior, called emergence, was monitored by the Tracor Acoustic Profiling System (TAPS) with six frequencies (265–3000 kHz) to clarify the mechanisms of benthic-pelagic coupling. Instead of one emergence event up to the surface at night, data with high spatial resolution indicate multiple emergence events varying with both the size of the organisms and distance above the bottom, suggesting that for some species there is a target depth beyond which upward migration is limited. In the Damariscotta River estuary, ME, nocturnal emergence events of mysid shrimp, Neomysis americana, occur from late June through early November. Mysid shrimp are known to be important food sources for fishes such as longhorn sculpins, smelt, alewives, and Atlantic cod. The timing of their emergence near the bottom corresponds to the maximum flood tide, suggesting enhancing retention in the estuary. Smaller organisms, on the other hand, emerge primarily during periods of slack tide, but reach the surface only at slack low, also avoiding washout.